feat: add task phash

[be-marc]

task = tsk("spam")
resampling = rsmp("cv", folds = 3)
resampling$instantiate(task)

resample(tsk("pima"), lrn("classif.rpart"), resampling)

#> Error: DataBackend did not return the queried rows correctly: 3067 requested, 501 received

Would solve errors like this where the resampling tries to access rows that are not present because the resampling was instantiated on a larger task. In this PR, benchmark() and resample() check if the resampling was instantiated on the task. This is done with a Task$phash that excludes the features.

Would come with an overhead especially in fselect due to the additional hash operations

[be-marc]

If we want this, we need to check #1198

[be-marc]

The error message has been extended with the sentence "The resampling was probably instantiated on a different task". I will close this PR for now.